Legend of trick encasing prone individual (7)
I believe the answer is:
caption
'legend' is the definition.
(synonyms)
'trick encasing prone individual' is the wordplay.
'trick' becomes 'con' (a con is a fraud or trick).
'encasing' is an insertion indicator.
'prone' becomes 'apt' (I've seen this before).
'individual' becomes 'i' (Roman numeral for one).
'apt'+'i'='apti'
'con' going around 'apti' is 'CAPTION'.
'of' acts as a link.
(Other definitions for caption that I've seen before include "Pontiac (anag)" , "Brief description of an illustration" , "Text under photo" , "Elegance of dress" , "Provide (a picture) with a title" .)